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1 بسم رلا هللارلا هللا This is the second histology lecture in the GI system. In this lecture, we will discuss the histology of the esophagus, stomach, and small intestine so prepare yourself.this sheet only covers what the doctor said in his lecture; so, refer to his slides as you read this sheet. thnx Histology of the Esophagus - Esophagus: it is a muscular tube, its length is about 25cm. - from the incisor to the cardia of the stomach it takes about 45cm. - this is important for the gastroscope. gastroscope is divided as 10,15,20,25.. ect cm. - so when the Dr. sees it s now 45cm at the incisors, he knows that it reached reached the cardia of the stomach. - Histologically, the layers of the esophagus are: mucosa, sub-mucosa, muscularis externa(muscular layer) and connective tissue (adventitia or serosa) - Serosa covers about 1.2 cm of ir, which is the only part of esophagus in the abdominal cavity, it mostly lies in neck and thorax. For the esophagus, these are: 1-Mucosa, which consist of: -lining epithelium: stratified squamous non-keratinized. -lamina propria :loose connective tissue, it contains lymphatics, blood vessels and the most important content is the glands,so called esophageal cardiac gland (called cardiac in relation to the 1 st part of the stomach; the cardia) and its very common in the lower third before the stomach which has gastric glands in its lamina propria also. - In histology they re no abrupt changes in the structure of connected tissues, that s why the histological structure of the lower third of esophagus is so similar to that of the stomach. -Muscularis mucosa: which is basically two ribbons of smooth muscle (outerlongitudinal, inner-circular) but because it's very thin, may not be visible... not really well-developed here as in other organs. 2- Submucosa: its significance in GI tract, contains lymphatics, blood vessels and in some organs like the esophagus it has glands. most of the sub-mucosa of the esophagus contains esophageal glands proper, we can find them in the upper, middle, and lower thirds (the lower third also contains cardiac gland in its lamina propria). 1

2 3-Muscularis externa: in the GI tract this layer is divided into outer longitudinal and inner circular, between them is the myenteric plexus or Auerbach's plexus (parasympathetic and sympathetic). In physiology they consider it a separate nervous system and depend on reflex, but here in anatomy the parasympathetic part is connected to the CNS, it s secretomotor for glands and stimulate smooth muscle peristaltic movement. while the sympathetic is vasomotor for blood vessels and cause vasoconstriction. 4- Adventitia: Connective tissue found in most of the esophagus (ex: neck, thorax and the small part in the abdomen after it pierces the diaphragm through an opening called esophageal orifices,that s located one inch to the left at the level of T10, carried with the esophagus through this opening the two vagi (right & left), but when they enter the diaphragm they become anterior & posterior. Now the Dr. gives a brief explanation about this pic. The type of secretion for esophageal gland is seromucous. The type of glands is tubular (may be straight or branched) In the esophagus, the upper third is voluntary ( with striated muscle), the middle third contains both smooth and striated muscle cells, while the lower third has only smooth muscle cells. therefore, histologically you can determine which area of the esophagus you're looking at (upper, middle,or lower third ) according to the type of muscle cells you identify. Stomach : divided into 4 parts : 1- fundus 2- cardia: which works as a physiological sphincter because it prevents regurgitation of the chyme, but NOT an anatomical one, because there is no thickening in the smooth muscle layer. 3-body 4-pylorus (pyloric canal & pyloric sphincter ). NOTE :Histologically,the fundus and body are identical but they are different from the cardia and pylorus. 2

3 - Mucosa of stomach contains 4 types of cells: 1- Parietal cells for secreting HCL and intrinsic factor ( required for absorption of vitamin B12 in the ileum. 2- Chief cells: secrete pepsinogen,which is converted into pepsin, and gastric lipase. 3- Mucous cells: secrete the mucous 4- Gastrin cells (endocrine cells) : secrete gastrin hormone. The layers of the stomach are the same, we have : 1-mucosa, 2- sub-mucosa, 3- muscularis externa, 4- serosa ( with simple squamous covering epithelium (mesothelium) ) We now turn back to the mucosa for a more detailed discussion of its layers: Mucosal layers: 1-lining epithelium or surface epithelium : The epithelium covering the surface and lining the pits is a simple columnar epithelium, which is different than that of esophagus. 2-lamina propria filled with gastric gland which have ducts called gastric pits which are invaginations of the gastric epithelium, gastric glands contain the four aforementioned types of secretory cells. ** NOTE : oblique sections don t show all the ducts, some of them are seen and others looks circular or oval. what are the comparisons between body, cardia and pylorus? depends on lamina propria and the size of the gland and the size of the ducts(gastric pits). pylorus: long ducts, small glands, tubular glands, simple or usually columnar, and coiled secretory portion. body: large glands, short ducts,the type of gland is tubular simple or usually branched. 3-muscularis mucosa (two rebounds of smooth muscle ). Mucus consists primarily of water (95%), lipids, and glycoproteins, which in combination form a hydrophobic protective gel. Bicarbonate secreted by the surface epithelial cells into the mucous gel, forms a ph gradient ranging from 1 at the gastric luminal surface to 7 along the epithelial cell surface. surface epithelial cells prevent autodigestion; bicarbonate and mucous decrease effects of HCl and protect the mucosa. 3

4 Cardia: **The cardia is a narrow circular band 1-2cm long, and1.5 3 cm in width. at the transition between the esophagus and the stomach. **Its mucosa contains simple or branched tubular cardiac glands. **The terminal portions of these glands are frequently coiled, often with large lumens.(we can see coiling in cardia and pylorus) **Most of the secretory cells produce mucus and lysozyme (an enzyme that attacks bacterial walls), but a few parietal cells secreting H+ and Cl (which will form HCl in the lumen) can be found. **These glands are similar in structure to the cardiac glands of the terminal portion of the esophagus. Fundus and body : the glands are large and take up a large part of the lamina propria, but the gastric pits are short,some books say 2/5-3/5 of the length. each gastric gland has three distinct regions: the isthmus, neck and base. especially in the body, majority of mucous cells are in the isthmus. parietal cells mostly in the neck but in other sites are also found. chief cells are found in the base where we also find enteroendocrine cells (gastrin cells) in the neck and isthmus: you also find stem cells that are responsible of mitosis and regeneration (in 4-6 days after damage in mucous cell)... stem cells move upwards or downwards to replace other degenerative cells. under the light microscope the most seen cells are : 1- mucous cells 2- parietal cells (find most between isthmus and neck) and the parietal cells are acidophilic which secrete HCL & appear pink in color. 3- chief cells are most common in the base which has chief cells with large amount of ribonucleic acids and RER are basophilic and appear dark in color. Now lets do a brief review : The isthmus : close to the gastric pit, mainly contains Mucous cells(in the body), also find stem cells. the neck: mainly contains parietal cells, also find stem cells. the base: mainly contains chief cells. 4

5 Stem Cells: Found in the isthmus and neck regions but few in number.gland has simple columnar cells but in different types of cells. Are there goblet cells in the stomach? no. these are unicellular glands that secrete mucus which start in small intestine and increase distally, but in stomach no goblet cell just simple columnar mucus cell. These cells have a high rate of mitosis; some of them move upward or downwards to replace the degenerative cells, which have a turnover time of 4-7 days. Mucous Neck cells : Mucous neck cells are present in clusters or as single cells between parietal cells in the necks of gastric glands. Their mucus secretion is quite different from that of the surface epithelial mucus cells. They are irregular in shape, with the nucleus at the base of the cell and the secretory granules near the apical surface. in preparation by eosin stain, has a foamy appearance after dissolving of mucous like a vacuoles (as all mucous secretary cells appear foamy). Parietal cells : parietal cells present in the surface epithelium at the neck of the gland, faint or acidphilic in appearance. While at the base of gland is dark basophilic chief cell. parietal cells have two stages : resting stage: no HCl production. These stage contains tubulovesicles, the common component of cell are tubules and vesicles. active stage: produce HCL and converted into intracellular canaliculus, contain HCl towards the apex of the cell. parietal cells are responsible for secretion of HCL through parasympathetic: a secertomotor system of myennetric plexus from the vagus nerve ( make the parasympathetic fibers) which synapses in myenteric ganglia. Postganglionic fibers : very very short in the wall and goes to smooth muscle and gland. 5

6 In the past they used to consider the hyperacidity is the cause of peptic ulcers. so, The surgery focused on the vagus nerve and cut it, to prevent the acidity and gastric ulcer. but, nowadays it been discovered that a bacterial called helicobacter pylori is responsible of peptic ulcer. Chief (zymogenic) cells: above (in the gland) you see parietal cells which are acidophilic, rounded with nucleous and are very clear. but chief cells have zymogenic granules towards the apex while the base is basophilic which has mitochondria and ribonucleic acids, and secrete pepsinogen and gastric lipase. Enteroendocrine cells: In the stomach they re G-cells or gastric cells (a type of enteroendocrine cells), secreting gastrin hormone. It appears the lumen in the middle with nucleus and other structures. NOW we finished the body and fundus, we give a huge explanation about body& fundus cause they take a large part of the whole stomach. Pylorus: - Consist of pyloric canal and pyloric sphincter, sphincter means thickening of circular smooth muscle which is different than cardia (cardia is a physiological sphincter only, no thickening of smooth muscle). - The difference between pylorus and body is that gastric pits are very long but gastric glands are thin. Because, most of the digestion occurs in the body and in the pylorus the digestion decreases. pylorus functions to passes the chyme to the duodenum, and most of the digestion occurs in the body. - The type of gland is: tubular coiled glands, may be branched or simple. The lamina propria it contains lymphatic nodules. lymphocytes when scattered has no significance. but, when it gathered it appears like lymphatic nodule and this indicates an effect (an action). lymphatic system helps in immunity because it s possible that the food we eat contains bacteria, viruses, dusts etc. so, the lymphatic nodules in pylorus engulf these foreign bodies. 6

7 important note: pylorus cell, does it have parietal or chief cells? No it doesn t, what distinguishes it that it has a few parietal cells (some books say no parietal cells). when we see a section in the lab, we don t see parietal nor chief cells.mostly we see mucus cells whether in glands or at the surface. we find mucus cells to balance the body's acidity and the chyme as it passes to the duodenum ( although the duodenum rich in bicarbonate and mucous to balance the acidity to prevent duodenal ulcer in the first inch). Briefly about the other layers : The submucosa is composed of dense connective tissue containing blood and lymph vessels; it is infiltrated by lymphoid cells, macrophages, and mast cells. for pylorus and body: muscularis externa in stomach have 3 layers, (usually we have outer longitudinal and inner circular) but here you find: the internal layer is oblique The middle layer is circular, and you should know that at pylorus the pyloric sphincter comes from thickening in the middle circular smooth muscle. The external layer is longitudinal The stomach is covered by a thin serosa, which is simple squamous epithelium. Histology of the small intestine - Consists of three parts: *duodenum *jejunum *ileum the difference between them that duodenum its retroperitoneal ; while, jejunum and ileum are intraperitoneal and have mesentery (two layers of peritoneum surrounding the jejunum and ileum). The length of the small intestine is between 5-6 m. The function mainly if for digestion and absorption especially the duodenum which receives the bile salts from gall bladder and liver, and also the secretions of pancreas which, both open in the second part of duodenum in pancreatic duct and common bile duct. In the small intestine the mucosa has finger-like projections called intestinal villi between mm to increase surface area. Plicae circularis (Kerckring's valves): projection from lamina propria which enter through the mucosa to increase surface area. 7

8 The layers of small intestine are also the same: mucosa which has lamina propria and muscularis mucosa. lamina propria also filled with glands called crypts of Lieberkühn, it has different cells the same as the stomach. The distinguishing factor of small intestine : it has goblet cells and every time we go distally it increases (increase gradually). They are most numerous in the large intestine for lubrication. the submucosa: duodenum is the second organ which contains gland, called Brunner's glands, secrete alkaline secretion for neutralization of the acidity of the stomach. muscularis externa: inner circular, outer longitudinal, and also myennetric plexus for secretion and motility of the small intestine (peristaltic movement). Duodenum has leaf-shaped projections while in jejenum and ileum: finger-like projection. Intestinal glands (crypts of lieberkuhn) with the villi have a continuation (the lower half is glands, upper is villi ), An indication of this is that lining epithelium for gland and surface are simple columnar epithelium cells and goblet cells. look at the Diagram: The villi of small intestine extend from the surface. In the villi : o you find cells (simple columnar epithelium cells) and goblet cells o lymphatic capillary (lacteals): blind-ended lymphatic capillary: for absorption of lymph or fat. o also blood vessels: capillaries in villi o villi's inside has lamina propria, rich in lymphatic&blood capillaries o scattered lymphocytes and goblet cells o surface is striated because of microvili extruding on the surface. o as for the gland (bottom left): also has goblet cells 8

9 o type of cells: simple columnar epithelium o also has mucous cells and enteroendocrine cells o the base: paneth's cells whose base is clear with a nucleus and apical granules found especially in jejenum and maybe in the ileum. the apex of villi: striated or brush border come from the microvilli: Each absorptive cell is estimated to have an average of 3000 microvilli, and 1-2 mm of mucosa contains about 200 million of these structures. The presence of plicae, villi, and microvilli greatly increases the surface of the intestinal lining. It has been calculated that plicae increase the intestinal surface 3-fold, the villi increase it 10-fold, and the microvilli increase it 20-fold. Together, these processes are responsible for a 600-fold increase in the intestinal surface, resulting in a total area of 200 m2 Goblet cells: Goblet cells find in the surface and in the gland, begins in the duodenum and increases in number as they approach the ileum. Goblet cells function to protection and lubrication. Paneth's Cells: Find in the basal portion of the gland, has secretory granules at the apex of the cytoplasm whose function is secreting lysozyme which is antibacterial and protect the flora of the intestine. The end Please forgive me for any mistakes. Best of luck سر من أسرار النجاح) 5 دقائق( DONE BY: Malak Shbeta 9